1. Field of the Invention
The present invention relates to infrared sensors and methods for producing the infrared sensors. In particular, the present invention relates to, for example, an infrared sensor including an infrared-sensing portion having a sensing electrode on a substrate made of a thermoelectric conversion material and a method for producing the infrared sensor.
2. Description of the Related Art
FIGS. 19A to 19C are illustrative views of an exemplary method for producing an infrared sensor in the related art. To produce the infrared sensor, as shown in FIG. 19A, a substrate 3 made of, for example, Si is prepared. A lower electrode 1 is formed on the substrate 3. A vitreous layer 2 is formed thereon. A Pb thin film 4 is deposited by evaporation on a bonding surface of a PbTiO3-based pyroelectric substrate 5. The Pb thin film 4 on the pyroelectric substrate 5 is brought into contact with the vitreous layer 2 on the substrate 3. Heat treatment is performed at about 600° C. to about 1,000° C. to enable the vitreous layer 2 to react with the Pb thin film 4 to form a low-melting-point vitreous layer 6, thereby stacking the pyroelectric substrate 5 on the substrate 3. Then, as shown in FIG. 19B, the thickness of the pyroelectric substrate 5 is reduced by polishing. A light-receiving surface electrode 7 is formed by sputtering to form an infrared-sensing portion. As shown in FIG. 19C, an insulating film 8 made of, for example, SiO2, is formed on the pyroelectric substrate 5 provided with the light-receiving surface electrode 7. The substrate 3 located on a portion at which the light-receiving surface electrode 7 is arranged is removed by etching to form a Si-substrate-removal portion 9.
In such an infrared sensor, since the pyroelectric substrate 5 is bonded to the substrate 3, the thickness of the pyroelectric substrate 5 can be reduced. The formation of the Si-substrate-removal portion 9 prevents thermal conduction from the portion at which the light-receiving surface electrode 7 is arranged to the substrate 3. Thus, when infrared energy is incident on the infrared-sensing portion, the temperature of the infrared-sensing portion is significantly changed. This results in improved thermoelectric conversion efficiency and responsiveness. Furthermore, the infrared-sensing portion can have a very small thickness, so that a heat conduction path is narrowed. Thus, adjacent infrared-sensing portions can be spaced apart at shorter intervals, which results in a greater packing density. Moreover, in a multi-element sensor including a plurality of infrared-sensing portions, the remaining substrate 3 located between adjacent infrared-sensing portions can function as a heat sink, thereby providing a small multi-element sensor that is not significantly influenced by crosstalk (see, for example, Japanese Unexamined Patent Application Publication No. 6-194226).
However, in such an infrared sensor, the pyroelectric substrate is in contact with the Si substrate, except at the infrared-sensing portion. This provides insufficient thermal insulation. Thus, the thermoelectric conversion efficiency and responsiveness are inadequate.